In the prior art, a disk brake can be applied on a traction machine of an elevator, with its structure shown in FIG. 1 and FIG. 2. It comprises a brake disk (1), a moving disk (2), a fixed disk (3), left and right friction plates (15, 16), a brake coil (4), a brake spring (5), a bolt (6), a spring bulkhead (7), a small spring (8), a guide rod (9), a sleeve (10), a first locknut (11), an adjusting bolt (12), a mounting base (13), and a brake calipers (14); wherein, the brake coil (4) and brake spring (5) are arranged in the fixed disk (3); the brake calipers (14) are fixed to the fixed disk (3) with screws; the moving disk (2) and the fixed disk (3) are connected in series in a movable manner with bolts, and the working clearance between them is adjusted to be A; the left and right friction plates (15, 16) are on each side of the brake disk (1) and attached to the inner side of the moving disk (2) and brake calipers (14), respectively; a mounting hole is arranged on the brake calipers (14), the sleeve (10) is arranged in the mounting hole, and the guide rod (9) is inserted in the sleeve (10) and mounted on the mounting base (13); the small spring (8) and the spring bulkhead (7) are fitted over the front end of the guide rod (9) in sequence and fixed to the guide rod (9) with the bolt (6); the adjusting bolt (12) is screwed on the rear end of the brake calipers (14), the spacing between the head of the adjusting bolt (12) and the mounting plane of the mounting base (13) is adjusted to be A/2, and the adjusting bolt (12) is locked tight with the first locknut (11).
When the disk brake is in braking state (as shown in FIG. 1), the brake coil (4) is cut off from power, the brake spring (5) pushes the moving disk (2) so that the working clearance A is formed between the moving disk (2) and the fixed disk (3); meanwhile, the left and right friction plates (15, 16) at the inner side of the moving disk (2) and brake calipers (14) clamp the brake disk (1) to prevent the brake disk (1) from rotation. When the disk brake is to be released (as shown in FIG. 2), the brake coil (4) is charged, so that a magnetic circuit is formed in the working clearance A between the moving disk (2) and the fixed disk (3) and electromagnetic force is created, and thereby the moving disk (2) and the fixed disk (3) attract each other; during the process of moving under the attraction force, the brake calipers (14) drive the fixed disk (3) to move towards the mounting base (13) at the same time under the spring force of the small spring (8) on the front end of the guide rod (9); however, since the spacing between the adjusting bolt (12) on the rear end of the brake calipers (14) and the mounting plane of the mounting base (13) is only A/2, the brake calipers (14) can only drive the fixed disk (3) to move A/2 distance backwards; whereas, since the total working clearance is A, the moving disk (2) moves A/2 distance outwards; the final result of the movement is: the working clearance A is allocated between the two sides of the brake disk (1), so that the left and right friction plates (15, 16) at the inner side of the moving disk (2) and the brake calipers (14) are no longer clamping the brake disk (1), and therefore the brake disk (1) can rotate freely.
FIG. 3 is a reference diagram of the working state of the aforementioned disk brake when it is mounted on a traction machine, wherein the brake is fixed to a front cover (19) of the traction machine via the mounting base (13), and the brake disk (1) is connected to a traction wheel (18) of the traction machine and is fitted over a main shaft (17) of the traction machine.
The working state of the traction machine is: a steel rope is hung on the traction wheel (18), the elevator cabin is dragged to move up or down under the frictional force between the steel rope and the traction wheel (18); when the elevator lands on a floor and the door of the elevator cabin is opened, the disk brake is cut off from power and thereby clamps the brake disk (1) to realize braking; when normal operation of the elevator is required, the disk brake is charged and releases the brake disk (1), so that the brake disk (1) can rotate with the traction wheel (18) normally.
The working clearance A in the disk brake in such a structure is very small; according to the calculating formula of electromagnetic force:
      F    =                                        S            ×                          B              2                                            8            ×            π                          ×                  10          7                    =              4        ⁢                                  ⁢                  SB          2                ×                  10          5                          B    =                            μ          0                ×        H            =                        μ          0                ⁢                              N            ×            I                    L                        F—Electromagnetic force;    B—Magnetic induction intensity;    S—Cross-sectional area of magnet;    L—Length of the air clearance, i.e., working clearance A;It can be seen from the above formula: the electromagnetic force is inversely proportional to the squared value of the air clearance; therefore, the smaller the air clearance is, the stronger the electromagnetic force will be. Compared with other types of brakes, when the same electromagnetic force is required, disk brakes can be manufactured in smaller size; in other words, disk brakes have an advantage of achieving high electromagnetic force. However, the small working clearance A causes some drawbacks as well: when the elevator cabin is hung onto the traction wheel (18) on the traction machine, the traction wheel (18) bears radial force F, which also acts on the main shaft (17) and thereby causes some bending deflection on the main shaft (17); as a result, the brake disk (1) results in inclination, and therefore the acting point of the disk brake has some displacement and inclination, following the inclination of the brake disk (1).
Here, the effect of displacement is mainly discussed: if the diameter of the brake disk (1) is large, the displacement will be comparable to the size of the working clearance A; since the brake is mounted on the front cover (19) of the traction machine and the mounting plane of the front cover (19) is fixed, the brake has to move along with the displacement of the braking point of brake disk (1), because the brake clamps the brake disk (1); as a consequence, the distance between the end face of the adjusting screw (12) on the rear end of the brake calipers (14) and the mounting plane of the mounting base (13) is no longer A/2; the change of the distance causes uneven distribution of the working clearance between the two sides of the brake disk (1) when the brake is in charged state, and the brake disk (1) will chafe the friction plate at one side and produce noise; when the chafed friction plate is worn to a certain degree, it cannot be used to realize effective braking, and therefore brings potential safety hazards. Moreover, commercial traction machines with disk brakes available in the market usually have to be debugged on site after the elevator cabin is hung onto the traction machine; however, the adjustment of the aforementioned clearance must be done by a professional technician; such adjustment work adds a big expense in the installation on after-sale service of products. Furthermore, the axial displacement of the brake disk (1) will vary with the load in the elevator cabin, and therefore the brake cannot be tuned up to the normal state.
In the Chinese Patent Publication No. CN100385134C, a caliper type brake with a releaser is disclosed. To release or center the caliper type brake relative to the brake disk, the technical scheme of the caliper type brake employs a twin-arm rocker rod/rocker frame, which is supported on a fixed pin shaft (i.e. the guide rod) in a revolvable manner; one tongue piece of the rocker rod is connected to the circumferential surface of an armature disk (i.e., the moving disk), and the other tongue piece is connected to the brake calipers. Specifically, when the brake releases, the rocker rod turns the displacement of the moving disk into the movement of the brake calipers in the reverse direction, so that the journey at each side of the brake disk is equal to half of the total clearance. However, as described above, when the brake is mounted on the traction machine and the load is attached to the main shaft of the traction machine, the main shaft will have some bending deflection and therefore cause some inclination on the brake disk; as a result, the brake disk has some horizontal displacement and inclination; when the brake is in braking state, since there is clearance between the guide rod and the sleeve, the brake will incline with the brake disk, and therefore the total clearance in the horizontal direction is smaller than A. When the brake is charged, the brake releases the brake disk; under the action of the rocker rod, the displacement of the moving disk is turned into the displacement of the brake calipers, and the brake is recovered to vertical state without inclination; however, since the brake disk is still kept with some inclination, the clearances formed by the brake calipers at the sides of the brake disk are uneven. During that process, the displacement of the brake calipers in vertical direction at different positions is not constant completely; instead, the displacement is half of the total journey of the brake calipers only when the brake calipers are in the middle position between the left and right friction plates. In addition, in a specific embodiment of that invention, one tongue piece of the rocker rod is fixed to the circumferential surface of the moving plate, while the other tongue piece is fixed to the upper part of the brake calipers; however, in such a caliper type brake, the clearance cannot be halved accurately between the two sides of the brake disk, due to the irrational fixing points of the rocker rod structure and uneven stress. Furthermore, when the bending deflection reaches to a certain degree, the clearance even cannot be allocated correctly.